new without a clue :/

hi im new here and new to growing, its my first grow, im pairing up with a friend who has 3 sucsesful grows already behind him, im "veging" 7 chemdogs at the minute heading into there third week today, and my friend is going to flower them, he doesnt live exactly next door infact not even the next town so hes only up once a week maybe once a fortnight, so im turning to you guys to help me out inn my hours of need!!!!!!! 5 plants are growing well and are ready to be transfared to pots tuesday! 2 however are really really slow and one has yellow on the end of its leaf, im growing under a 90w blue ufo LED and on top of a heat mat, i didnt put up any dollar for the seeds so i dont wana waste them on me friend, i am however going to get a plant or 2 each harvest so itl be worth my while too! does that make sense????? stoned typing! oh yeah i do vigorously ph the water and even make sure its at room temp, more pics to follow if requested my cameras acting up

are you using nutes? do you have a thermostat connected to your mat? and do you keep the medium wet or do you let them dry out?

I would say the two small plants aren't worth keeping in my opinon, just one of those things. I would just focus on the good looking ones, and when you transplant, which I only do once, don't be shy about the depth, especially the leggy one. Looks like the other plants are doing fine by the looks of them. Good luck.